Typewriting machine



Nov. 9, 1937. R. G. THOMPSON I 2,098,319

TYPEWRITING MACHINE Filed May 25, 1934 3 Sheets-Sheet 1 FIGJ;

ATTORNEY NQV. 9, 1937. R. s) THOMPSON 1 3 TYPEWRITING MACHINE Filed May 25, 1934 3 5.8 5 hwet 2 INVENTO Nov. 9, 1937. R. G. THOMPSON TYPEWRITING MACHINE Filed May 25, 1934 3 Sheets-Sheet 3 A+TORNEY Patented Nov. 9, 1937 TYPEWRITING MACHINE Russell G. Thompson, Rochester, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application May 25, 1934, Serial No. 727,382

11 Claims. (Cl. 197-127) This invention relates to typewriting machines in general.

A broad object is to provide a novel paper feeding device for typewriting machines.

Another broad object is to provide a novel paper severing device for typewriting machines.

An object is to provide paper feeding and severing mechanism whose operation is automatically initiated at the end of a line of writing.

A further object is to provide paper feeding and/or severing mechanism which is operated by power.

Another object is to provide paper feeding and/or severing mechanism automatically operated by the carriage return mechanism of a typewriting machine.

A further object is to provide paper feeding and/or-severing mechanism whose operation is fully automatic and requires no attention by the operator of the machine other than to insert the end of a fresh strip of paper when that previously "in the machine becomes exhausted.

A specific object is to provide paper feeding and/or severing mechanism which is extremely simple in construction and hence may be manufactured at low cost.

Another specific object is to provide paper feeding and/or severing mechanism which can be installed on existing typewriting machines without materially altering suchmachines or interfering with their usual functions.

A specific object is to provide paper severing mechanism which can be moved to a non-eflective position to enable the machine to be used in the 35 ordinary way, that is, for writing on single, manually inserted sheets.

Various other objects, advantages and features of the inventiomwill be pointed out in the following description and claims, or will be apparent 40 from a study of the description, claims, and drawings.

In the drawings:

Fig. 1 is a top plan view of a typewriting machine showing the present invention attached to such machine.

Fig. 2 is an enlarged vertical section on the line 2-2 in Fig.1.

Fig. 3 is an enlarged vertical section on line 50 3-3 in Fig. 1.

Fig. 4 is an enlarged vertical section -on line 4-4 in Fig. 1.

Fig. 5 is a perspective view of the carriage return mechanism and parts of ing mechanism.

the platen rotat- Fig. 6 is a plan view of the escapement mechanism.

Fig. 1 of the drawings shows the present invention attached to a power driven typewriter now well-known in the art as the Electromatic. The 5 various mechanisms of this machine have been described in a large number of patents of which No. 1,602,757 describing the power typebar operation, No. 1,681,267 the motor driving connections, and No. 1,753,450 the automatic carriage return mechanism will provide suflicient information regarding the general details of construction of the machine to enable those skilled in the art to understand the present invention. Only a very few details of the above mechanisms and a very general description of their operation will be given herein as the cited patents are sufliciently detailed to understand the general operation of the machine.

The usual keyboard is provided having character keys I!) (Fig. 1) corresponding to which are pivoted typebars II. The latter are operated, as in Patent No. 1,602,757, by means of cams (not shown) which coact with a power roller 12 (Fig., 5) to move the typebars to the printing point. The .power roller I2 is rotated continuously by a motor (not shown) which is connected to a shaft l3. Suitable worm gearing ll connects shaft I 3 with a short shaft l5 to which power roller I2 is removably connected so as to be driven by the 30 motor. When a switch lever I 6 (Fig. 1) is moved toward the rear of the machine, the motor is started and drives shaft I5 and roller l2 continuously as in Patent No. 1,681,267. Shaft I5 also drives the carriage return mechanism.

The carriage I! is mounted for movement transversely of the machine on a front rail l8 and a rear rail l9 which rails are grooved as usual to guide anti-friction rollers and are secured to the. main frame of the machine. The carriage comprises side plates 20 integrally joined by a channel-shaped member 2| (Fig.2) which is grooved to receive suitable rollers or balls 22 which mount the carriage on rails. l6, l9. Rotatably mounted in the frames 20 is across rod 23 which supports the platen pressure rolls as will be explained here-. inafter. A tie rod 24, a tabular stop bar 25, and a marginal stop bar.26 secured to frames 20 rigidly Join frames 2| so that a sturdy carriage results.

The bar 25 has notches cut therein at letter space intervals in which notches the usual tabulator stops 21 may be inserted as desired. Marginal able marginal stops 28, 29 in any desired positions as usual in typewriting machines. The specific details of the bar 26 and stops 28, 29 are of no importance herein, as they are not, by themselves, part of the present invention but may take any suitable form. The stop 28 is the right-hand marginal stop while stop 29 is the left-hand marginal stop. 7

The platen 30 is of usual construction and is mounted on a shaft 3i supported by suitable bearings in frames 20. Pivoted as at 32 (Fig. 2) to each side frame 20 is an arm 33 to which is secured the usual paper table 34. A spring 35 secured to one of the arms 33 and to the adjacent side frame 20 normally holds the paper table 34 in the position of Figs. 1 and 2 but it may be raised and swung backwardly until arms 33 strike rod 24. Spring 35 will swing past the pivot 32 when the paper table-is so raised and have the effect of holding arms 33 against rod 24.

Cross rod 23 is loosely mounted in side frames 20 and at its mid-point carries an arm 36 formed from sheet metal and bent to form a stirrup on which rests a rod 31 mounted in ears forming part offa sheet metal paper guide 38. The latter carries two cross rods 39 on which are loosely mounted front platen pressure rolls 4|] and rear pressure rolls 4|, the pressure rolls projecting through suitable rectangular openings in the paper guide 38 into contact with platen 33. A spring-acting upon an arm (neither of which is shown in the drawings) secured to rod 23 tends to rock rod 23 and arm 36 in a clockwise direction thus applying pressure to the center of rod 31. Thus the rolls 40, 4| are pressed evenly against the platen. The usual combined line gauge and paper guide 42 is loosely mounted on rod 23 and is spring pressed against the platen and guides the work sheet to the printing line.

Mounted on the underside of the member 2| is an escapement rack 43 which co-operates with any desired form of escapement for advancing the carriage a letter space after each type bar has made its impression at the printing line or when the usual space bar is operated. This escapement mechanism is not involved herein except in a minor respect to be explained hereinafter, hence no detailed description of the escapement mechanism will be necessary.

The carriage is returned after each line has been written by mechanism similar in principle and in most details to that described in Patent No. 1,753,450. It is controlled by a carriage return key 44. (Figs. 1 and 4) which, when depressed, causes a single lobed spiral cam 45 (Fig. 5) to rotate slightly until it is gripped by the roller i2. After tl'Fs occurs the roller l2 rotates said cam to cause a bell crank assembly 46 to be rocked clockwise on a pivot rod 47! (Fig. 5) thereby straightening toggle 4B. This causes clutch operating arm 49 to squeeze together friction clutch elements connecting the carriage return tape drum 50 to shaft l5. Rotation of drum 53 causes the carriage return tape 5| to be wound on the drum thereby drawing the carriage ii to the right (Fig. 1) until stopped by engagement of left-hand marginal stop 29 with a lug 52 in a stop lever 53 pivoted at 54 to the rear rail is, thus arresting the carriage in position to begin a new line of writing. Shortly before this occurs, a downwardly projecting part of the mar-- ginal stop 29 rides onto a cam surface 55a on one arm of a lever 55 also pivoted on rail l9 and causes said arm to be depressed. As a result a rod 56, attached to the other arm of lever 55 and to One arm of a bell crank 51, is drawn to the left thus rocking said bell crank 51 in a direction to draw rearwardly a rod 58, pivoted to the other arm of hell crank 51 and to one arm of a bell crank 59 pivoted at 60 to the frame of the machine.

The bell crank 59 will be rocked clockwise (Fig. 5) causing one arm 6i thereof, which extends under an arm 48a forming part of toggle 48, to bend the'toggle and thereby effect disengagement of the friction clutch elements. Thus the tape 5i ceases to pull the carriage to the right an instant before the left-hand marginal stop 29 strikes lug 52.

When a line is being written in the usual fashion the' carriage moves to the left. Eventually the right-hand marginal stop will strike lug 52 and rock stop lever 53 a slight amount in a coun terclockwise direction (Fig. 5). This causes a rod 82, pivoted to stop lever 53 and to one arm of a bell crank 53, to be drawn to the left, rocking bell crank 63 counterclockwise and drawing rearwardly a link 64 pivoted to the other arm of bell crank 63 and to an arm 65 forming part of the carriage return key 44 which is pivoted at 66. It is plain that the carriage return key will be automatically depressed to initiate operation of the carriage return mechanism at the end of each line of writing.

In the present invention the tape 5! is connected to a drum which is rotated to feed the platen a predetermined amount prior to automatically severing the length of paper thus fed by the rotation of the platen.

The mechanism so far described, save for the drum mentioned in the last sentence and parts associated therewith, is substantially the same as the "Electromatic typewriter now on the market and extensively used.

The tape 5| passes over a guide pulley 61 mounted on the main framework of the machine, over a pulley 68 (Figs. 4 and 5) mounted in a. bracket 63 secured to member 2|, and is secured to a drum i0 loosely mounted on shaft 3| adjacent the left end of platen 30 (Fig. 1). A spiral spring H, mounted in the interior of drum 1i] and secured to the latter and one of the hearing sleeves 12 supporting shaft 3 I, normally tends to rotate drum Ill in such direction as to wind the tape 51 on said drum (clockwise Figs. 3 and 4).

Pivotally mounted on the right side of drum in adjacent the end of platen 30, is a driving pawl 73 having the shape shown in Fig. 3. A spring 14 connected to the tail of pawl 13 and a pin carried by drum ill normally holds the tail of pawl 13 against the hub of drum Til. Secured to the left-hand end of platen 30 adjacent drum 10 is a disc 75 having diametrically opposite, radially extending lugs 16 out of the path of pawl 13, and diametrically opposite, axially extendinglugs ll in the path of movement of pawl 13. The flat ends of lugs it are inclined slightly to form a cam surface while one axially extending edge of each lug T! is bevelled slightly as shown in Fig. 3.

Pivoted on a stud 18 carried by the left-hand frame 28 (Figs. 3 and 5) is a pair of stop pawls i3, 83 having bent over lugs 81!, 32 in the path of movement of lugs 16 and pawl "iii. The lug at is at the right of the lower lug 16 (Fig. 3) while the lug 82 is at the left of said lug E6. The pawl extends to the rightunderneath lug 8,! (Fig. 5) and is held in this position by a light spring 83 while a spring 84' somewhat stronger than spring 83, holds pawl 19 in the position shown in Fig. 3.

' A pin 85 carried by left-hand frame 23 may be provided to prevent pawl I9 from getting into the path of lugs 11. Ordinarily, however, the balance between springs 83, 84 and a spring 88 attached to a release lever 81 pivoted on a stud 88 carried by left-hand frame 28, will be suflicient to keep the pawls I9, 88 in the normal position of Fig. 3. The lever 81 is formed like a short bail and has an arm 89 which is pressed downwardly on pawl I9 by spring 86 and also has a stop arm 98 overlying a stop pin 8| carried by frame 28. 4

Normally the lugs 8|, 82 of pawls I8, 88 prevent rotation of the platen manually by means of the usual knobs 82 secured to shaft 3|. When lever 81 'isgrasped and pulled forward (to the right in Fig. 3), both pawls I9, 88 are depressed far enough to clear the lug i8 engaged by said lugs 8|, 82 before the arm 88 strikes pin 9|. The platen will then be free to turn in a counterclockwise direction.

Secured to the side of drum I8 is a stop 83 which is out of the path of lugs I6, I'I but is adapted to strike lug 8|. Normally the tension of spring II forces stop 93 against lug 8| as in Fig. 3 and this prevents rotation of drum 18 in response to spring li. When pawls I8, 88 are manually depressed by lever 81 as described above to permit manual rotation of the platen, the stop pin 9| prevents the pawl 18 from moving downwardly far enough to clear the stop 83.

The operation of the foregoing mechanism will now be described. When operation of the carriage return mechanism is initiated, the pull exerted by the tape 5| will, before any movement of the carriage takes place, cause drum 118 to rotate in a counterclockwise direction (Figs. 3 and 4) approximately two-thirds of a revolution. When stop 93 on drum I8 has moved away from lug 8| approximately one-sixteenth of a revolution, a bevel or cam surface 84 in pawl 13 first strikes lug 82 and rocks pawl 88 downwardly, then strikes lug 8i and cams it downwardly far enough to disengage said lug from lug I6 thus freeing the platen for subsequent rotation. Pawl 13 next engages the lower lug I7 and by such engagement commences to drive the platen 38 in acounterclockwise direction which movement will continue until the platen 38 has completed exact- 1y one half-revolution. During the first part of this movement; pawl 13 will clear lug 82 permitting spring 84 to restore pawl I8 to the position of Fig. 3 with lug 8| in the path of movement of the upper lug' I8 in said figure. Near the end of the above movement of platen 38, the cam surface in the upper lug 18 will engage lug 82 and depress said lug permitting the lug 16 to pass lug 82 and engage lug 8| and when this occurs further rotation of the platen is positively prevented. At this point the carriage begins to move and will be restored to position to begin a new line as previously described. When the carriage is fully returned the carriage return clutch is disengaged by the action of the left-hand marginal stop and drum 58 ceases to pull the tape and is free to rotate on shaft I5. Spring 1| then becomes effective; to rotate drum I8 in a clockwise direction back to the position of Fig. 3 where stop 93 again engages lug 8| and prevents fur- I tween platen 38 and pressure rolls 48, 4| will be fed forward a distance equal to half the circumference of the platen 38 each time the carriage return mechanism is operated,. regardless of whether 'such operation is manually initiated by key 44 or automatically initiated by marginal stop 28. 1

In addition to rotating the platen to feed a work sheet the carriage return mechanism operates cutting mechanism for severing a strip into predetermined lengths, the severing taking place after a line of writing has been made on the strip. This mechanism is shown in Figs. 1 and 2.

Secured to the paper table 34 is a box-like structure generally designated 95 in the drawings. It is composed of a one-piece U-shaped frame comprising a back 86 bolted to paper table 34 by bolts 81 and two side pieces 88 bent at right angles to the back 96, and a cross frame piece 99, spaced from the back 96, and secured to sides 88 as by brazing, spot welding, or in any other desired way. Secured to the back of cross frame 88 are curved paper guides 89a which may be of spring steel and extend downwardly and rearwardly (Fig. 2) we point in the rear of platen 38. The parts of sides 98 which overhang platen 38 have formed therein lugs I88 which extend at right angles to sides 98. Frame piece 99 has a flange or apron I8I formed therein which extends to right and left of the box-like structure. Secured to the front of the apron I8I is a knife blade I82 and a paper deflector I83 spaced from each other a distance slightly greater than the maximum thickness of paper which can be used in the machine, bolts like I84, at each end of the knife I82 and paper deflector I83, securing them to apron I8I.

Secured to the cover I85, which forms part of the cabinet enclosing the machine and, as usual, is removable to permit cleaning of the machine, is a bracket I86. The latter is arranged to straddle the usual opening I 81 in cover I 85 through which opening the type bars move inprinting upon the work sheet and overhangs the platen at the printing point as shown in Figs.

1 and 2. Pivoted ona stud I88 carried by the left side of bracket I86 is a member I89 having a lug |I8 bent at right angles thereto the plane of which lug is substantially perpendicular to the plane of knife I82 and parallel with the cutting edge of such knife. Joumaled on a stud III on the lug H8 is a disk II2 having a beveled edge forming .a knife and coacting with knife I82. Conveniently the disk II2 may be termed a slitting knife or cutter. A spring II3 connected to pins on member I89 and bracket I88, respectively, tends to rock such member counterclockwise so as to cause the side of slitting knife H2 to bear firmly but not too heavily on the cutting edge of knife I82.

The operation of the mechanisms described between guides 89a and back 86 and pushed down to a position to be gripped between rollers 48, 4| and platen 38. To facilitate this operation the usual release lever II5 (Fig. 1) may be drawn forwardly, rocking rod 23 and arm 36 counterclockwise thus permitting the strip II4 to be pushed around the platen until the leading edge engages deflector I83 and is guided into the space between said deflector and knife I82. The leading edge (which may have been previously squared as by means of shears) is positioned coincident with the cutting edge of slitting knife I82. After the strip has been so positioned its longer edges should be parallel with the sides 98 but not quite touching them in order to avoid binding in feeding operations. Lever H5 is then released to permit the feed rolls 40, M to press to strip II4 against platen 30.

The marginal stops 28, 29 are positioned to limit travel of the carriage from the starting position of Fig. 1,-to a position where knife II2 overlies the right-hand end of slitting knife I02 which is extended to the right of right-side 90 a somewhat greater distance than the left-hand end of said knife from the left-side 98. Thus movement of the carriage is confined to a distance slight y greater than the maximum width of strip II4 that can be inserted between the sides 98.

The operator, by manipulating the proper keys I0, next writes a line on the strip II4. As the carriage moves from right to left (Fig. 1) in response to the usual escapement mechanism, knives I02, '2 will move relative to each other until when the last character is imprinted knife II2 will have moved a distance relative to knife I02 which will depend on the number of characters p'rinted plus the number of letter spaces separating the words or characters printed on the strip. It will be assumed that a line has been written extending from the position of Fig.

1 to within a few letter spaces distance of the right-hand edge of strip II4 so that knife II2 bears on the edge of knife I02 opposite the lastto cause knife II2 tomove far enough to bear upon the extension of knife I02 but, to save time and ensure a quick positive action of the lever 53 which initiates the return of the carriage, it is preferred to omit a number of teeth from escapement rack 43, as shown in Fig. 6, so as to cause the carriage to jump a distance suflicient to remove knife I I2 from the path of the strip I I4.

This movement causes the lever 53 to initiate operation of the carriage return mechanism. The pull of tape 5| first causes the platen 30 to be rotated as described, thereby feeding the strip II4 a distance equal to half the circumference of platen 30, and then causes carriage H to be drawn to the right until arrested by the left-hand marginal stop. During the return movement of carriage I! the knives I02, II2 will co-operate to cut off that part of the strip II4 which was previously fed above the apron IOI and the severed portion will drop into the shallow pocket formed between sides 98, frame 99, apron IOI, and lugs I00. This pocket, as shown in Fig. 2 is large enough to accumulate several dozen of the checks or tickets cut by knives I02, II2.

These checks or tickets can be used for a variety of purposes such as coupons, store orders, index cards, requisitions, receipts, and so on. In the illustrative embodiment of the invention, the checks are cut to'approximately thesame size as standard 3" x 5" index cards. Obviously the size will depend on the proportions of the parts. Owing to the simplicity of the mechanism and its automatic operation the checks can be written very rapidly as all the operator is required to do is to operate the keys I to write a line.

It may be found undesirable in some cases to omit the teeth from rack 43 as described, as

on full width sheets or where the line of writing does not always extend the full width of the strip H4. The same results can be obtained by operating the usual tabulating key II6 (Fig. 1). This will cause the carriage to move rapidly to the left until the stop 28 strikes lever 53.

It has been found by experience that in spite of the simplicity of the mechanism the feeding and cutting mechanisms operate very accurately and feed and out the strip I I4 into lengths which are so uniformly cut that little or no difference in length is observable.

When it is not desired to use the cutting mechanism but to write single lines on bills, invoices, orders or similar single sheets, the paper table can be raised and the sheets inserted by hand in the usual fashion between platen 30 and rolls 40, 4I. This is possible because paper guide 38 is extended upwardly and to the left (Fig. 2) sufficiently to provide a throat or passage to guide the inserted sheet between said platen and rolls. The cover I can be removed whenever it is desired to clean the machine or make minor adjustments or repairs without disturbing the working relation of the parts.

The invention can easily be applied to machines manufactured prior to the present invention as all that is necessary is to drill the necessary holes for bracket I08, bolts 91, and the pins I8, 88 or the assemblies on which these parts are to be mounted can be very quickly replaced by assemblies including the necessary parts. The simplicity of construction enables the invention to be manufactured very cheaply and installed with little labor and expense.

While there has been shown and described and pointed out the fundamental novel features of the invention as applied to a single modification, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention therefore to be limited only as indicated by the scope of the following claims.

What is claimed is as follows:

1. In combination with a platen, a platen driving element comprising a rotatable tape drum, a tape wound thereon; a driving element mounted on the tape drum and effective to drive the platen when the tape drum is rotated by pulling the tape wound thereon in a direction to unwind the tape, said element being ineffective when the tape drum is reversely rotated; a spring secured to the tape drum for reversely rotating the drum to rewind the tape when pull on the latter is relaxed, a pair of holding pawls for normally preventing rotation of the platen and releasable by initial movement of said element, and stops mounted on the platen and co-operating with said holding pawls to limit rotation of the platen.

2. In combination with a rotatable platen, means for holding the platen against rotation, a platen rotating device, and means carried by said device and operative to drive the platen, said means being also operative during the initial movement of the rotating device to release the holding means.

3. In combination with a rotatable platen, means for holding the platen against rotation and a platen rotating device comprising a tape drum, a draw band secured to the drum and adapted to rotate the tape drum when a pull is exerted on said band, and a platen driving element carried by said drum, said element co-operating with the holding means to release the latter during initial movement of the drum in response to a pull exerted on the tape.

4. In combination with a rotatable platen;

means for rotating the platen including a tape drum, a tape connected to said drum to rotate the platen when a pull is exerted on the tape; a driving element adapted, when the drum is rotated; to engage the platen and rotate it; and a holding device normally efiective to prevent rotation of the platen, said device being releasable by initial movement of the driving element and adapted to limit rotation of the platen by the tape drum.

5. In combination with a rotatable platen, means for holding the platen against rotation, a platen rotating device, and means carried by said device and operative to drive the platen, said means being also operative during the initial movement of the rotating device to release the holding means, and a manual device for releasing the holding means to permit rotation of the platen by hand.

6. In combination, a feed roller, means for normally holding the feed roller against rotation,

- means to rotate said feed roller and having an idle initial movement before rotation of the feed roller commences and means actuated by the rotating means for releasing the holding means during the initial idle movement of the rotating means.

7. In combination, a feed roller, means for locking the feed roller against operation, a tape drum operatively associated with the feed roller, a tape secured to the drum and arranged to rotate the drum when a pull is exerted on the tape, and a driving element adapted after the drum has turned a predetermined extent to couple the platen to the tape drum for rotation by said drum, said element having a part thereof engageable with the locking means to release the latter to permit subsequent rotation of the feed roller by said drum.

8. In combination, a feed roller, a driven element secured to the feed roller and having a locking lug and a driving lug, a pair of locking pawls engaging the locking lug to prevent rotation of the roller, a tape drum coaxial with the roller, a tape secured to the drum and arranged to rotate said drum when a pull is exerted on the tape, and a driving element carried by said drum and adapted to engage the driving lug to positively rotate the roller, said driving element having a cam portion adapted to cam the locking pawls out of engagement with the locking lug prior to engagement of the driving element with the driving lug.

9. In combination, a feed roller, a driven plate secured to the feed roller and having a locking lug and a driving lug, a pair of locking pawls engaging the locking lug to prevent rotation of the roller, a tape drum coaxial with the roller, a tape secured to the drum and arranged to rotate said drum when a pull is exerted on the tape; a driving element carried by said drum and adapted to engage the driving lug to positively rotate the roller, said driving element having a cam portion adapted to cam the locking pawls out of engagement with the locking lug prior to engagement of the driving element with the driving lug; means to rotate the roller manually, and a release lever for manually releasing the holding pawls to permit manual rotation of the roller.

10. In combination, a feed roller; releasable detent means for normally preventing rotation of the feed roller and adapted, when the roller is rotated, to limit the extent of rotation of the roller to a predetermined amount, means to rotate said roller; and means operated by the rotating means and adapted to momentarily release the detent means during the initial operation of the rotating means to permit rotation of the roller by the rotating means and further adapted to permit the detent means to return to effective position to limit subsequent rotation of the roller. 11. In combination, a feed roller, a tape drum coaxial with said roller, a detent for locking said roller against rotation; means connecting said tape drum and roller whereby rotation of the tape drum in one direction drives said roller and permitting reverse rotation of said drum without aifecting the roller, said means being operative during the initial rotation of the tape drum to release the detent to permit rotation of said roller by said tape drum; a tape wound on said drum and arranged to rotate said drum in a direction to rotate the roller when a pull is exerted on the tape to unwind the latter from the drum, a coil spring for reversely rotating the drum to rewind the tape thereon, and a stop secured to the tape drum and cooperating with the detent to limit the reverse movement of the drum.

' RUSSELL G. THOMPSON. 

